Vacuum switch



Max-zh 6, 1962 c. JOHNSON 3,024,329

VACUUM SWITCH Filed Nov. 9, 1959 I le?) .L5 93 "521 l\\ 55 wo )f is INV TOR.

@mais l dif/wav lllnitedl States Patent C) Filed Nov. 9, 1959, Ser. No. 851,764 Claims. (Cl. 20G-87) This invention relates to switching devices, and more particularly to an improved vacuum switch.

More specifically, this invention relates to vacuum switches of the type employing a movable armature and a pair of ixed contacts within an evacuated envelope. In this type of switch, the armature, which carries a contact element therewith, is normally positioned with the contact carried thereby being in engagement with one of the fixed contacts. The armature is adapted to be moved to a position wherein the contact carried thereby engages the other contact within the envelope. Such movement is effected magneticallyas by energizing a toroidal coil placed over the envelope to set up a magnetic dield to attract the armature to the desired position.

In pn'or art high-vacuum switches, it 4is Ia common practice to assemble the armature and contact elements in a glass envelope. In thus assembling these elements, it is necessary to position them so that the contact carried by the armature will, in the normal position of the armature, engage one xed contact with sucient rmness to maintain such engagement during vibration. Also, it must be possible with a predetermined magnetic tield strength, i.e., a predetermined current in the toroidal coil, to attract the armature to its other position, and in such other position to insure that engagement of its contact with the other ixed contact will be maintained during vibration.

To properly orient and secure the elements in a glass envelope requires the services of a highly skilled worker. Not only is this objectionable because of the high cost of production, reliance on the particular worker makes quantity production impossible. Further, many assem* bled switches have to be rejected because of errors made in assembly, all of which makes the cost unduly high.

Prior art vacuum switches have numerous other disadvantages. One such disadvantage resides in the fragility of glass, land in the inherent variations in the wall thickness of the glass envelope. These characteristics contribute to breakage or rupture of the envelope, particularly when it is subjected to extreme vibration and shock.

Another disadvantage of prior art vacuum switches is that they cannot be made with as high a vacuum as is desired. This is for the reason that the glass envelope cannot be heated to a high temperature while it is evacuated. Due to the relatively low melting temperature of glass, heating lduring vacuum processing must be kept to relatively low temperatures. Accordingly, when the envelope is sealed oit, there is still considerable gas trapped within it. The getter technique eliminates some of this residual gas, but an undesirable amount still remains within the envelope.

Further disadvantages of prior art vacuum switches using glass envelopes are revealed in mounting them onto a support. For example, where the switch is to be mounted on a metal casing, a metal lband is secured to the glass envelope. This band is then secured to the metal casing, as by soldering. Such operations require the application of heat in the vicinity of the envelope which adversely aects the glass. The seal between the metal ring and the envelope may be broken, and the envelope itself may be melted. Thus, although a satisfactory vacuum switch may be constructed, the effectiveness of the switch may be destroyed in mounting it onto a support.

Itis an object of this invention to, provide a unique vacuum switch which utilizes no parts, such as glass orv the like, having low melting points.

It is another object of this invention to provide anI construction with. which` a' higher vacuum can be obtained in assembly thanv'is 110simproved vacu-um switch sible with prior art vacuum switches.

A further object of this invention is to provide a vacuum switch wherein stationary and movable contacts to be located within an evacuated housing or envelope can be selectively positioned and adjusted prior to enclosing them in the envelope.

A still further object of this invention is to provide a vacuum switch structure which can be assembled in a minimum of time by relatively unskilled laborers.

It is yet another object of this invention to provide a' vacuum switch structure having a minimum number of component parts of simple design and rugged construction, capable of quantity production and having uniform characteristics.

The above and other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying `drawing of illustrative embodiments thereof, in which:

FIGURE l is a combined schematic illustration of my vacuum switch and a block `diagram of circuits controlled therewith;

FIGURE 2 s a partial sectional view of the cup element of the switch, showing the arrangement of a pair of Xed contacts and an armature carrying a movable contact;

FIGURE 3 is a longitudinal sectional view of the contact and armature elements disposed in a sleeve housing, showing the parts arranged preparatory to evacuating the housing;

FIGURE 4 is a perspective View of a non-magnetic insert which forms part of the housing, such insert being shaped to insure movement of the armature in a predetermined direction under the iniluence of a magnetic field;

FIGURE 5 is a partial sectional View of the upper portion of the housing after it has been evacuated, showing how the terminal connection is made thereto;

FIGURE 6 is a perspective View of a modiied insert adapted for use in the housing of my switch;

FIGURE 7 is a schematic diagram illustrating the switch utilizing the insert of FIGURE 6 for selectively controlling the positions of one or more of a plurality of movable armatures toward respective stationary contacts, and illustrating schematically its use for selectively utilizing one or more portions of a circuit; and

FIGURE 8 is a sectional view of the upper portion of an envelope for the contacts shown in FIGURE 7, showing a non-magnetic closure element supporting terminal posts connected to respective movable contacts.

Referring to FIGURE 1, the switch of my invention is shown in use for controlling the operation of one or the other of a pair of pulse forming networks 10, 11, which are shown schematically as enclosed in a casing 12. The pulse forming networks 10, 11 have respective input leads 13, 14 to conventional charging coils (not shown), and common connections 15, 16 to groups of capacitors spaced along the coils.

The connections 15, 16 form the output leads of the pulse forming networks 10, 11, and are connected, as at 17, to a terminal post 18 supported on the casing 12. The terminal post 1S is connected as shown, to one end of the primary winding 19 of a pulse transformer 20; the other end of the primary winding 19 is grounded, as shown. The secondary winding 21 of the pulse transformer 20 is adapted for connection to means (not shown) operable in response to pulses developed across such secondary windings, e.g., a magnetron oscillator which has a frequency of operation dependent upon the shape and duration of such pulses.

In order to effect operation of one or the other of the pulse forming networks 10, 11, a switch 25 is provided for connecting one or the other of the input leads 13, 14 to the output of a charging voltage source 26. To this end, the switch 21 is provided with a terminal lead 27 which is coupled to the source 26 through a choke 2S.

As will be described in greater detail hereinafter, the switch 25 is provided with a pair of xed contacts conJ nected to the leads 13, 14, and a movable contact connected to the terminal lead 27. The movable contact is adapted to be selectively moved so as to connect one lor the other of the leads 13, 14 to the terminal leads 27. To effect such movement of the movable contact a toroidal coil 311 is provided which is adapted to be connected through a switch 31 to an energizing source 32. With the switch 31 open, the movable contact is in a normal position wherein one of the leads 13, 14 is connected to the source 26. When the switch 31 is closed, the coil 30 is energized by the source 32 to eifect movement of the movable contact to a position wherein the other of the leads 13, 14 is connected to the charging source 26. In this manner, the pulse transformer 20 can be selectively coupled to one or the other of the pulse forming networks 10, 11, to thereby develop across the secondary winding 21 pulses having Ia waveform and duration determined by the characteristics of the particular pulse forming network connected to the primary winding 19.

The development of pulses is effected by periodically connecting the terminal leads 27 to ground, and to this end an electronic switch 34 is connected between the terminal lead 27 and ground. A trigger source 35 is provided which develops trigger pulses of a predetermined repetition rate. Upon the occurrence of each trigger pulse, the electronic switch 34 conductively connects the terminal lead 27 to ground, thereby allowing the discharge of the capacitors in the pulse forming network connected to the terminal lead 27 through the switch 25.

The construction of my switch 25 will now be explained with reference to FIGURES 2-5, along with FIGURE l. As shown, the lower end of the envelope of the switch 25 comprises a flanged cup or bowl shaped element 37 The cup 37 extends into the interior of the casing 12, with the rim 38 thereof abutting the top surface of the casing. Preferably', the cup 37 is formed of a high ternperature metal, such as cold rolled steel. Preferably, the rim 38 of the cup 37 is curved over (see FIGURES 2 and 3) so that the edge thereof is located below the upper portion of the cup. The edge of the cup is secured to the casing 12, as by silver soldering it in place.

The fixed contacts previously mentioned rare shown in FIGURES 2 and 3 at 40 and 41. As shown, the contacts 40, 41 are disposed at the upper ends of respective lengths of conductive rnetal rods 42, 43 which extend at their upper ends through beads 44, 45 of ceramic tubing which are secured in the lower end of the cup 37, preferably by silver soldering. The ends 42', 43 of the rods 42, 43 extending below the beads 44, 4S are connected to the leads 13, 14 to the pulse forming networks 10, 11 whereby to connect the fixed contacts 40, 41 to the re spective leads 13, 14. Disposed between the rods 42, 43 is a thin rod 46 which at its lower end is secured in a ceramic bead 47 xed in the bottom of the cup 37. At least the upper end of the rod 46 is a conductive contact portion 46 which extends between and above the contacts 40, 41, and an insulating element, illustrated as a ceramic disc 4S, is secured to the contact 46' at a point intermediate its upper end and the portion thereof which is disposed between the contacts 40, 41. The rod 46 may be a length of conductive spring wire, or it may be comprised of conductive and non-conductive elements brazed together.

As shown in FIGURES 2 and 3, the conductive rods 42, 43 are shaped so that the rod 46 has a normal position wherein the contact 46 engages the contact 41 on the rod 43, and is spaced from the contact 40.

Referring to FIGURE 3, the rods 42, 43, 46, and the disc 48 are surrounded by a sleeve 50, the lower end of which extends into the cup 37 `and is secured thereto. The lower end of the sleeve 5t) is shown to be of smaller diameter than the inner diameter of the cup 37, and is outwardly ilarecl, as at 52. The periphery or rim of the flared portion 52 is secured to the inner wall of the cup 37, as by silver soldering or copper brazing.

The portion of the sleeve 50 that is surrounded by the coil 30 is formed of a tube of magnetic material which contains a non-magnetic insert 54. The insert 54 separates magnetic sections, indicated at 55 and 56, and is positioned so as to surround the disc 48 mounted adjacent the upper end of lthe rod 46. The insert 54 and the magnetic sections 55, 56 are made of high-temperature materials', for example, the insert 54 may be formed of copper and the magnetic sections 5S, 56 formed of steel tubing,

Secured to the ceramic disc 48, as by copper brazing, is a ring 58 of magnetic material, such as iron. The iron ring 48 constitutes an armature element which is to be attracted, upon energization of the coil 30, in a direction to separate the contact 46" from the contact 41 and to bring the contact 46 into engagement with the contact 40. The insert 54 is so shaped and positioned as to insure this result, as will now be explained.

As shown, the insert 54 is in the form of a cylinder which at one end has been cut diagonally (see FIGURE 4 along with FIGURES l and 3) so as to provide a tubular element having diametrically opposed portions 54', 54" of minimum and maximum length. The insert 54 is positioned intermediate the sections 55, 56 so that the portion 54 of minimum length is located at the portion of the sleeve nearest the contact 40. This position of the insert 54 insures that, upon energizing the coil 30, the armature 58 will be attracted toward the portion 54 of minimum length to effect the desired engagement of the contact 46 and the contact 40.

As will be apparent, the magnetic lines of force established by the coil 30 pass between the magnetic sections S5, 56 through the insert 54. However, that half of the insert 54 on the left-hand side of IFIGURE 3 offers less reluctance to the lines of force than does the right-hand half of the insert. Accordingly, there is a greater' concentration of the magnetic lines of force immediately adjacent the portion 54 of minimum length, thereby causing the armature 58 to be attracted in the direction of such portion 54 and causing the contact 46 to engage the contact 40.

In order to connect the movable contact 46 to an output connection, such as the terminal lead 27 in FIGURE l, an elongated conductive element 60, such as a length of copper ribbon, is connected at one end to the upper end of the movable contact 46. The conductive element 60 is connected to a short tube 61 of conductive material at the top of the envelope 50. The tube 61 is secured in the upper end of a tubular element or sleeve 62 of insulating material which is secured at its lower end, as by copper brazing, to the upper end of the magnetic section 55. The lower end of the tube 61 is flared outwardly and has the peripheral surface of the rim secured, as by copper brazing, to the interior of the insulating element 62.

Preferably, the insulating element 62 is formed of material capable of withstanding rather high temperatures. For this purpose the element 62 may be made of alumina, an aluminum oxide compound capable of withstanding temperatures in the neighborhood of 2000 F. The lower end of the element 62 is supported within the upper end of the section 55 of the envelope as on a shoulder 63. As with the connections between various elements as previously described, the insulating element 62 is secured to the section 55 with material capable of withstanding extremely high temperatures, eg., silver soldering or copper brazing.

With the parts arranged as shown in FIGURE 3, I place the assembly in an oven and connect the open end of the tube 61 to a vacuum system. Since all of the parts are capable of withstanding rather high temperatures, evacuation can be carried out with at temperatures well above the melting temperature of glass, eg., vacnum processing at ltlflt)o F, to 2000 F. Accordingly, my switch structure is `such that it can be substantially completely evacuated, and to a degree not obtainable with glass envelopes even with the use of the getter technique.

`When the desired vacuum has been obtained, the upper end of the tube 61 is pinched (see FIGURE 5), as at 65, thereby sealing olf the interior of the envelope. Thereafter, I place over the tube 61 a tight itting cup 66 of conductive material which is secured at its lower end, as by copper brazing, to the interior of the insulating element 62. The cup 66 is closed at its upper end, and it has embedded therein a terminal post element 67.

Thus, with the terminal post 67 connected to the terminal lead 27 in FIGURE 1, it will be seen that the source 26 is connected to one of the pulse forming networks 10, 11 through the terminal post 67, the cup 66, the tube 61, the conductive element 60, `and thence through the contact 46 and the one of the contacts 40, 41 engaged thereby.

Not only does my vacuum switch constitute a much more rugged structure than switches employing glass envelopes, but it can be assembled in a minimum of time by relatively unskilled workers. Unlike the procedure with prior art vacuum switches, the contacts 40, 41 and 46 are positioned properly while freely accessible, i.e., before placing the sleeve 5t) over them.

The rods 42, 43 are characterized in that they can be bent, but they will retain their shapes. For this purpose, the rods 42, 43 may be made of nickel tubing. The rod 46 preferably is a relatively stiff, spring metal member. Initially, the rod 43 is bent so that the contact 41 thereon abuts the contact 46 of the rod 46. In this connection the rod 46 is not straight when the contact 46 thereon engages the contact 41. Instead, the position of the rod 43 prevents the rod 46 from assuming a straight position, i.e., the rod is slightly eXed in its normal position of engagement with the contact 41. This means that, due to the spring characteristic of the rod 46, it bears against the stationary contact 41. The degree of ilex of the rod 46 determines the amount of force with which the contact 46 hears against the contact 41,

Both of the rods 42, 43 are bent by the worker as necessary to adjust their positions so that, in the normal position of the rod 46, the contact 46 bears against the contact 41 with the force necessary to withstand vibrations and shock of predetermined magnitudes, and so that the Contact 46 is held against the contact 46 under a predetermined yforce of attraction of the armature 53, as above described, despite vibrations and shock. Regarding vibrations and shock, the proper position of the contact 41 can be determined by controllably vibrating the cup 37 to the extent it is desired to maintain the contact between the contacts 46', 41.

To determine the force needed to cause the contact 46 to move from the contact 41 to the contact 4&1, an initial determination is made of the mechanical force which is the equivalent of the force of attraction of the armature that is 58 needed to so move the contact 46. A simple strain gauge is then attached to the upper end of the rod 46, and adjustments are made as necessary (by adjustably bending one or more of the rods 42, 43, 46) to obtain the proper reading on the strain gauge.

`Once the proper positions of the contact elements are obtained, the rest of the assembly is completed. Unlike prior art vacuum switches, there is no concern about whether the assembly of the rest of the switch will have any effect upon the settings of the contact elements. No

further manipulation of the contacts is needed, so that upon completing the assembly one is assured that they are properly positioned, and that they will operate properly.

FIGURES 6-8 illustrate means for employing my switch to actuate a plurality of contacts. In such a switch, the insert 54 previously described is replaced with an insert 70 (see FIGURE 6) of cylindrical construction. In `the embodiment shown, a cylindrical insert 70 comprises four spaced bars 7174 of non-magnetic material, ythe adjacent bars 71-72, 72-73, 73-74, and 74-71 having their mid-portions joined by curved band elements 75, 78 of non-magnetic material. Filling the remaining spaces between the bars 71-72, 72-73, 73-74, 74-71 are curved segments 80 of magnetic material.

With the insert constructed as shown in FIGURE 6, I utilize in my switch four spaced stationery contacts 811 which are positioned midway -between the respective pairs of adjacent bars 71-72, 72-73, 73-74, 74-71. Also, I utilize four spaced movable contacts 82455, each of which is located adjacent a respective xed contact 8.1.

It will be apparent that where I employ a plurality of xed contacts 81, such contacts are supported in the cup 37 in the same manner as the xed contacts previously described. Similarly, .the movable contacts 82-85 are the upper ends of respective rods extending from the base cup. Adjacent the tops of the movable contacts 8.2-85 are mounted respective armature elements 87, which are centered between the respective pairs of parallel bars 71`72, 72-73, 73--74, 74-71. Also, the armature elements 87 are located in the same plane as the nonmagnetic elements 75, 76, 77, 78.

The insert structure 70` is shaped to permit the armatures 87 to be individually attracted to effect engagement between the associated movable and xed contacts. To this end, I provide a plurality of generally U-shaped magnetic core elements 90. As shown in phantom in FIG- URE 6, the core elements 90 are arranged between the respective pairs of parallel Abars 71-72, 72-73, 73-74, 74-71, with the ends of the legs thereof confronting the magnetic elements 80 above and below the horizontal nonymagnetic elements 75-78. As shown, the space between the legs of fthe core elements 90 span the non-magnetic elements 75-78.

To establish a magnetic eld, respective coils 91 (see FIGURE 7) are wound around the core elements 90 intermediate their legs. Due to the arrangement of the nonmagnetic elements of the insert 70, energization of any coil 91 causes only the armature 87 immediately adjacent thereto to be attracted. This will be apparent upon study of one of `the sections; for example, if a magnetic eld is established in the core element 96 located between the bars 71, 72, the magnetic lines of force are concentrated between the faces of the coil element 90 and the armature 87 immediately `adjacent thereto. Accordingly, Ia strong attractive force exists to pull lthe adjacent armature 87 so that its contact 82 engages the fixed contact S1. The side bars 71, 72 of non-magnetic material prevent the lines of force from threading into the adjacent magnetic elements.

One use of the multi-contact switch arrangement is shown in FIGURE 7. A pulse-forming net-work is shown having a charging coil 93 and a plurality of spaced capacitive means connected lalong the coil, such capacitor means ybeing arranged in pairs 94, 95, 96, as by having the capacitor means of each pair connected together as at 97, 98, and 99. The output of the network is coupled to the primary winding 19 of the pulse transformer 29.

It is desired to operate the network so that (a) only 'the pair 96 is operative -to develop pulses across the primary winding 19, or (b) the pair 95 is operative with the pair 96 to develop pulses, or (c) all three pairs 94, 95, 96 are operative to develop pulses. My switch is adapted to eiect ythe necessary switching to connect the pairs in any of these combinations.

As shown schematically in FIGURE 7, the connection 99 is connected to one of the fixed contacts 81, the connection 98 is connected to Ia pair of the fixed contacts 81, and the connection 97 is connected to the rem-aining tixed contacts S1. The movable contacts 82, 85, are directly connected, as at 199, so that when these movable contacts are simultaneously in engagement with their respective fixed contacts 81, the connections 91, 98 will be connected together, i.e., the capacitive section 95 is operatively connected with the pair 96 between the coil 93 and the transformer 20.

The movable contacts 83, 84 are also directly connected, as at 1, so that when they simultaneously engage their respective fixed contacts 81, the connections 97, 98 are connected together. When none of the movable contacts 82, 85 engages its respective fixed contact 81, yonly the connection 99, i.e., to the capacitive pair 96, is ,coupled to the transformer 20.

To connect the capacitors, pairs 95, 96 together, the 'coils 91 of the cores 90 immediately adjacent the movable contact 82, 85 are simultaneously energized. This causes the movable contacts 82, 85 to engage their respective fixed contacts, thereby to connect both capaci-tors sections 95, 96 to the pulse transformer 20.

When it is desired to make all three capacitor pairs 94-96 operative, all of the coils 91 are energized, thereby to simultaneously connect all of the movable contacts 82-85 Ito their respective fixed contacts 81. In this manner, the pulse transformer 20 can be supplied with pulses .of any of three durations.

FIGURE 8 illustrates an arrangement of the top portion of my multi-contact switch for connecting the movable contacts to respective terminals. The upper portion `of the housing is formed by a non-magnetic tubular element 105 which has a small diameter tube port-ion 195 at its upper end. This tube portion 105 is pinched after evacuating to seal off the housing, in the same manner as the tube 61 of FIGURES 3 and 5. Respective elongated conductive elements 107 are led from the movable contacts to respective terminal posts 108 embedded in the element 105.

While I have described my invention with reference to particular embodiments thereof, it will be apparent that various modifications can be made without departing from the spirit and scope of my invention. Accordingly, I do not intend that my invention be limited, except -as -by the appended claims.

I claim:

1. -A switching device comprising: an evacuated housing including magnetic sections separated by a non-magnetic section, said non-magnetic section being shaped to permit magnetic lines of `force to pass into the housing and around said non-magnetic section from one magnetic section to the other; a pair of normally disengaged contact elements in said housing, one being fixed and the other movable, said xed contact being located between said non-magnetic section and said movable contact, said movable contact being attracted by said magnetic lines of force to move toward said non-magnetic section and engage said fixed Contact.

2. A switching device comprising: a pair of spaced stationary contacts and a movable contact therebetween, said movable contact normally engaging one of said stationary contacts; a magnetic element connected to said movable contact; an evacuated housing enclosing said contacts and elements, said housing having a pair of sections of magnetic material separated by a section of non-magnetic material, said non-magnetic section being located adjacent the stationary contact that is not engaged by said movable contact; and means to establish a magnetic field between said magnetic sections to thread past said non-magnetic section and through said magnetic element, whereby said magnetic element is attracted in a direction to move said movable contact from engagement with said one stationary contact and into engagement with the other stationary contact.

3. A vacuum switch comprising: a cup element; a pair of spaced conductive elements extending into said cup element and each having one end secured in and extending through the bottom of ysaid cup element, said conductive elements having respective contacts at their upper ends; an elongated element of conductive spring material secured at one end in the bottom of said cup element and extending at its upper end past the upper ends of said conductive elements, said elongated element being disposed between said conductive elements, said elongated element normally engaging one of said contacts; a magnetic armature element supported on the upper end of said elongated element; an elongated, evacuated housing having a sleeve surrounding said conductive and elongated elements, one end of said sleeve extending into said cup element and being secured to the interior thereof, said sleeve including a pair of sections of magnet-ic material separated by a section of non-magnetic material, said non-magnetic section surrounding said armature element, the lateral surface of said non-magnetic section varying in length, the portion of shortest length being positioned so that the other of said contacts is intermediate said elongated element and said portion of shortest length; a tubular element of non-magnetic material secured at one end to the upper magnetic section of said sleeve; a tubular element of conductive material secured in the upper end of said non-magnetic tubular element, said conductive tubular element being closed at its upper end; a conductive element connecting the upper end of said elongated element to said conductive tubular element; and a cap element of conductive material covering said conductive tubular element and being secured thereto, said cap element having a terminal post extending from its upper end.

4. A vacuum switch comprising: a cup element; a plurality of lengths of conductive elements extending into said cup element and each having one end secured in and extending through the bottom of said cup element to provide external terminals, said conductive elements having their upper ends arranged in a circle, said conductive elements at their upper ends being provided with contact surfaces facing the axis of the circle; a respective elongated element of conductive material extending past each contact surface and located between said surface and said axis, each being secured at one end in the bottom of said cup element, the upper ends of said elongated elements extending above the upper ends of said conductive elements, each elongated element having a contact portion spaced from and confronting a respective contact surface; a respective magnetic armature element supported on the upper end of each elongated element; an elongated, evacuated housing having a sleeve surrounding said conductive and elongated elements, one end of said sleeve being secured to the interior of said cup element, said sleeve including a pair of sections of magnetic material separated by a section of non-magnetic material, said section of nonmagnetic material being in the form of a cage having a plurality of axially extending parallel ribs connected by a entral band, said cage .being positioned with said armature elements confronting said band; a tubular element of non-magnetic material secured at one end to the upper magnetic section of said sleeve, said tubular element being closed at its upper end, said tubular element supporting a plurality of terminal posts; and a conductive element connected between the upper end of each elongated element and a respective terminal post.

5. A vacuum switch comprising: a stationary contact and a movable contact, a magnetic element; means securing said movable contact and said magnetic element in fixed spaced relation; and an evacuated housing enclosing said contacts and magnetic element, said housing having two magnetic portions and a non-magnetic portion therebetween, said non-magnetic portion being positioned ad- 9 10 jacent said magnetic element, whereby a magnetic eld References Cited in the tile of this patent can be set up between said magnetic portions to pass UNITED STATES PATENTS around said non-magnetic portion and through said magy netic element, thereby to move said movable contact to gllxggd J g1g/t l an operatwe position with respect to sald xed contact. 5 2,834,846 Eaves et al. May 13, 1958 2,877,316 Peek Mar. 10, 1959 2,898,422 Peek Aug. 4, 1959 

